Building up a database of spectro-photometric standard stars from the UV to the near-IR: A status report

We present a project aimed at establishing a set of 12 spectro-photometric standards over a wide wavelength range from 320 to 2500 nm. Currently no such set of standard stars covering the near-IR is available. Our strategy is to extend the useful range of existing well-established optical flux standards into the near-IR by means of integral field spectroscopy with SINFONI at the VLT combined with state-of-the-art white dwarf stellar atmospheric models. As a solid reference, we use two primary HST standard white dwarfs. This ESO "Observatory Programme" has been collecting data since February 2007. The analysis of the data obtained in the first year of the project shows that a careful selection of the atmospheric windows used to measure fluxes and the stability of SINFONI make it possible to achieve an accuracy of 3- 6% depending on the wavelength band and stellar magnitude, well within our original goal of 10% accuracy. While this project was originally tailored to the needs of the wide wavelength range (320-2500 nm) of X-shooter on the VLT, it will also benefit any other near-IR spectrographs, providing a huge improvement over existing flux calibration methods.